As the Internet continues to grow, high-capacity switches and routers are needed for backbone networks. Several approaches have been presented for high-speed packet switching systems. Most high-speed packet switching systems use a fixed-sized cell in the switch fabric. Variable-length packets are segmented into several fixed-sized cells when they arrive, switched through the switch fabric, and reassembled into packets before they depart.
For implementation in a high-speed switching system, there are mainly two approaches. One approach is a single-stage switch architecture. An example of the single-stage architecture is a crossbar switch, where identical switching elements are arranged on a matrix plane. However, the number of I/O pins in a crossbar chip may limit the switch size. This makes a large-scale switch difficult to implement cost-effectively, as the number of chips becomes large. Another approach is to use a multiple-stage switch architecture, such as a Clos-network switch. The Clos-network switch architecture, which is a three-stage switch, is scalable. Three-stage Clos-network switches use small switches as modules in each stage to build a switch with a large number of ports and less hardware than that of a single-stage switch of the same size.